Electrostrictive actuator

ABSTRACT

Apparatus is disclosed for doing useful work with electroexpansive material which expands volumetrically in response to an electric field. The material is disposed in a chamber of a fixed volume slightly greater than the volume of the material at rest. The volume intermediate the material and the chamber is filled with a fluid having good insulation properties. When the material expands in response to an electrical signal, insulating fluid is forced out of a passage in a wall of the chamber and performs work by actuating a plunger or diaphragm. Means, such as an intermediate piston, may be employed to isolate the insulating fluid from the hydraulic fluid in a device being thus hydraulically driven, such as a pump valving means or fluid control valve.

= nite States atet SlGNAL 5001266 Primary Examiner- Robert M. WalkerAttorney-Lindinberg, Freilich & Wasserman ABSTRACT: Apparatus isdisclosed for doing useful work with electroexpansive material whichexpands volumetrically in response to an electric field. The material isdisposed in a chamber of a fixed volume slightly greater than the volumeof the material at rest. The volume intermediate the material and thechamber is filled with a fluid having good insulation properties. Whenthe material expands in response to an electrical signal, insulatingfluid is forced out of a passage in a wall of the chamber and performswork by actuating a plunger or diaphragm. Means, such as an intermediatepiston, may be employed to isolate the insulating fluid from thehydraulic flbid in a device being thus hydraulically driven, such as apump valving means or fluid control valve.

PATENTEDAUGIOIQTIV 3,598,506

sum 3 OF 3 slam 500C205 COR/WOC 6. OA/E/u.

INVENTOR.

[xx M) W .47 TOQA/EVS ELECTROSTRICTIVE ACTUATOR BACKGROUND OF THEINVENTION This invention relates to drivers for pumps, valves, actuatorsand the like, and more particularly to electroexpansively powereddrivers.

Such devices as pumps and fuel injectors have been devised based uponthe piezoelectric effect of certain materials. Upon application of anelectric field across such material, the material expands or contractsalong known axes, depending upon the polarity of the electric field.Therefore, in such piezoelectric devices the expanding and contractingmaterial is generally so disposed in a housing that the mechanical loadis transmitted directly by the material, thereby requiring a preciseconfiguration and low compliance for the load surfaces Anotherdisadvantage of directly driven devices is that the travel of the loadsurfaces is quite limited. To overcome that disadvantage, it has beencommon practice to so stack a plurality of piezoelectric elements thattheir cumulative piezoelectric expansion is more substantial. But that,of course, compounds the first problem since more precise load surfaceswith low compliance are then required.

Some materials known as electrostrictive material exhibit the propertyof a positive dimension change in a direction parallel to the appliedelectric field regardless of the polarity of the applied field, withonly a second order reduction in dimensions along two complementary(orthogonal) directions. In other words, given the direction of theapplied electric field as the principle axis. the material will expandalong that axis regardless of the polarity of an applied voltage withvery little contraction along second and third mutually perpendicularaxes. Consequently, upon application of a voltage of either polarity,the material increases in volume sufficiently to perform useful work.

The present invention concerns the performance of useful work throughuse of any material, referred to hereinafter as volumetricelectroexpansive material," that is known to exhibit an increase involume in response to an electric field regardless of whether theincrease in volume is due to the piezoelectric effect or theelectrostrictive effect. The performance of work is best carried outhydraulically to avoid having mechanical loads transmitted throughmaterial interfaces.

An important advantage of a hydrostatically driven device using elementsof volumetric electroexpansive material is that the elements may beeasily produced, such as by casting, with loose tolerances in respect tosurface finish, compliance of interfaces, and mechanical strength of theceramic material, as well as dimensions. But of all the advantages ofsuch a device, the most important is that displacement amplification maybe readily achieved hydraulically even though that use ofelectroexpansive material would produce lower strains along a given axisfor a certain voltage gradient than in directly driven devices.

SUMMARY OF THE INVENTION According to the invention, anelectroexpansively powered fluid driver is provided by a body having achamber of a given volume and a passage in a wall thereof communicatingwith that chamber. Volumetric electroexpansive material is disposed inthat chamber but not to its full capacity. The space intermediate thevolumetric electroexpansive material and the chamber is filled with afluid so that when an electric field is applied across theelectroexpansive material, the material may undergo a total volumeincrease to perform work by forcing fluid from the chamber through thepassage in its wall. Such a fluid driver may be employed to pump fluid,either directly or by means of a piston.

A plurality of electroexpansive elements may be used to increase thetotal change in volume, i.e., to increase the hydraulic displacementproduced in response to an electrical signal.

The driver chamber may be of any suitable elongated configuration, suchas a cylinder to accommodate a stack of elements. The driver chamber mayalso be annular and the electroexpansive elements tubular.

Another configuration for the electroexpansive elements for the use in acylindrical chamber is a substantially segmental section. A plurality ofsegmental sections are disposed in the cylindrical chamber such thateach makes electrical contact with a split tube spring at the center.The split tube spring urges each of the segmental sections against thecylindrical wall of the chamber where a second electrical contact ismade to provide an electrical field in response to an electrical signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a longitudinal crosssection of a first embodiment of the present invention. 2 illustrates avariant of the first embodiment shown in FIG. ll.

FIG. 3 illustrates another variant of the first embodiment illustratedin FIG. ll.

FIG. 4 shows a longitudinal cross section of a second embodiment of thepresent invention.

FIG. 5 shows a cross section of a pump valving means for use with theembodiment of FIG. 4 in place of a valve element shown.

FIG. 6 illustrates a variant of the second embodiment illustrated inFIG. 4.

FIG. 7 shows a cross section of a third embodiment of the presentinvention.

FIG. 8 shows an isometric view of a segmental section ofelectroexpansive material employed in the embodiments of FIG. 7.

Fig. 9 illustrates a central column of nonconductive material with holesthroughout and a split ring of conductive spring material for use in theembodiment illustrated in FIG. 7 at the center of a plurality ofsegmental sections.

FIG. 10 illustrates in an isometric viewa variant of the embodimentillustrated in FIG. 7.

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionwill best be understood from the following description with reference tothe accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, thereis shown an electroexpansive driver body 10 comprising end plates 11 and12 and a cylindrical tube 13. Disposed within the driver body are aplurality of stacked elements made of volumetric electroexpansivematerial, such as element 114, each in the form of a disc. There are anumber of different materials commercially available that exhibit avolumetric electroexpansive effect in response to an electrical signal.Some suitable ceramic materials are Thin Loop" by Channel Industries ofSanta Barbara, California, and "Skinny Loop by Honeywell of Minneapolis,Minnesota.

A signal source 15 is connected across each of the stacked elements by,for example, soldering one terminal of the source 15 to the plate 12 andthe other terminal of the source 15 to a thin metal electrode interposedbetweeneach of the opposing faces of adjacent discs as shown. Alternatepairs of opposing faces are connected to the positive and negativeterminals of the source 15 in such a manner that each disc shares apositive electrode with one neighbor and a negative electrode with theother neighbor, the two electrodes at the stack extremities being of thesame polarity as the terminal of the source source 15 connected to theend plate 12. The plate 12 is made of suitable conductive material. Theplate 11 is in direct contact with the top of the stacked elements whilethe plate 12 is in contact with the bottom of the stack through a metaldisc 16 and a metal spring washer 17. The metal spring 17 holds theelements of the stack in electrical contact with the thin metalelectrodes interposed between adjacent discs. As electrical signals fromthe source 15 are applied, the stack continually expands, therebycontinually flexing the spring 17. The disc 16 protects the stack ofelectroexpansive elements from damage due to forces against the spring17-.

When an electrical signal is applied to the stack of electroexpansiveelements from the source 15, the total volume of the electroexpansivematerial disposed within the chamber of the body increases. Fluid withinthe chamber of the body 10 is thereby forced to flow under pressurethrough a passage 18 in the tubular wall 13 of the chamber. As theelectrical signal is removed, the total volume of the electroexpansivematerial descreases, thereby causing a reduction in pressure on theremaining fluid in the chamber of the body 10.

In order to pump fluid continually in response to electrical pulses,pump valving means 20 is connected to the passage 18. A one-way valve 21at the fluid inlet port 22 prevents fluid being forced from the chamberof the body 10 from being returned to its source. A one-way valve 23 inthe outlet port 24 similarly prevents fluid from flowing in the oppositedirection.

If the fluid being pumped is an electrical conductor, fluid in thechamber of the body 10 would provide a short circuit across theelectroexpansive elements. Accordingly, to pump conductive fluid, asleeve 26 of flexible material is provided around the stack ofelectroexpansive elements, from the plate 11 to the plate 12, to isolatethe fluid (which has suitable insulation properties) in contact with thestack of elements from the fluid pumped. In either case, a predeterminedminimum feed pressure at the inlet 22 would be required to insurefilling a pumping chamber 25.

FIG. 2 illustrates a variant of the first embodiment illustrated in FIG.I. The variation is substitution of a piston 30 for the flexible sleeve26 in the first embodiment of FIG. 1 to isolate the fluid being pumpedthrough the pump valving means 20 from fluid in the drive chamber of thebody 10. The volumetric electroexpansive elements, such as the elements14, are connected to a signal source as before.

As the electroexpansive material increases in volume, fluid is drivenfrom the chamber of the body 10 through a passage 18 against the piston30, thereby forcing fluid from the pumping chamber 25 through the outletport 24 of the pump valving means 20. As the electrical signal isremoved, the volume of the electroexpansive material decreases therebyallowing fluid to reenter the chamber of the body 10 as the piston 30 isdriven upwardly under the feed pressure of fluid at the inlet port 22.To minimize the feed pressure that would be required to insure fillingthe pump chamber 25 to its maximum, a return spring 31 is provided forthe piston in the pumping chamber 25. Since fluid to and from thepassage 18' must pass by the spring washer 17', holes (such as hole 32)may be provided in the washer 17'. Alternatively, notches may beprovided along the inner and outer edges of the washer 17', or radialbypass slots may be provided in the plate 12 or the disc 16.

Still another variant of the first embodiment of the present inventionis illustrated in FIG. 3. The principle variation is the provision of apiston 30 with a larger area exposed to the fluid being pumped than tofluid in the drive chamber of the body 10. In that manner, volumeamplification is obtained to increase the average flow rate from theinlet port 22 to the outlet port 24.

If force amplification were desired instead of volume amplification, thearea of the piston 30 in contact with the fluid in the chamber of thebody 10 would have been greater than the area in contact with fluidbeing pumped. In either case, the piston cylinder 34 (i.e., thecylindrical passage through the body 10 to the pump valving meanscontaining the piston 30') would have a large diameter portion ofsufficient length to allow maximum travel for the piston 30. A vent 33is provided at the base of the enlarged portion of the piston cylinderto facilitate driving the piston 30 down in response to an electricalsignal and up again in response to force of the return spring 31.Otherwise, a vacuum may be produced behind it as the piston 30' isdriven toward the pump chamber 25.

Another variation illustrated in FIG. 3 is provision of the body 10 andthe pump valving means 20 by integral metal castings of two longitudinalsections which are then welded, braised or otherwise fastened togetherin fluidtight manner after all of the internal elements have beenproperly placed. Electrical connections to the volumetricelectroexpansive element are made in a manner similar to that describedwith reference to the embodiment of FIG. 1.

Referring now to FIG. 4, a second embodiment of the present invention isprovided based on the dilation of volumetric electroexpansive materialin the direction of applied field without significant, if any,contraction on the two complementary axes. Both inside and outsidesurfaces of electroexpansive material (in the form of a tube) will thenact to displace fluid if the tube is placed within an annular chamber ofa body having a passage through a wall thereof. Thus, in the embodimentof FIG. 4, a body 40 is provided with an annular chamber 41 with apassage 42 from the chamber 41 to a piston cylinder 43 concentric withthe chamber 41. A signal source 45 is provided with one terminalconnected directly to the body 40 and the other terminal passing intothe chamber 41 where it is connected to the inner surface of a tube ofelectroexpansive material 44. The inside and ouside surfaces of the tube44 are coated with an electrically conductive coating, such as silver ornickel. The end surfaces of the tube 44 are coated with an electricallyconductive coating, such as silver or nickel. The end surfaces of thetube are not coated. It should be understood that the tube 44 ofelectroexpansive material is electrically insulated from the body 40 asby rings 46 and 47 of dielectric material. Springs are then placed onthe outside of the electroexpansive element 44, such as spring 48 formedfrom a band of conductive spring material, in order to maintainelectrical contact between the conductive coating on the outside surfaceof the electroexpansive element 44 and the body 40. To assure that fluidpressure will always be equal on both sides of the electroexpansiveelement 44, bypass slots are provided, such as a bypass slot 49.

A piston 50 is provided with an arm or stem 51 extending from the body40 in order to actuate a device as the piston 50 is moved up and downhydraulically in response to a signal from the source 45. As shown, thedevice is a valve 55 having two ports 56 and 57 through which fluid mayflow from one port to the other as the piston 50 is moved upwardly inresponse to a signal from the source 45. A spring 58 and nut 59 areprovided to adjust the position of the valve stem (arm or stem 51 of thepiston 50) to close the passage to the port 56 when no signal isapplied.

The embodiment of FIG. 4 may be readily adapted for pumping a fluid bysubstituting for the valve device 55 a pump valving device 60 issubstantially the same as the valve pumping means 20 illustrated in FIG.1, both in construction and in operation, and therefore will not befurther described with reference to the second embodiment of theinvention illustrated in FIG. 5.

FIG. 6 illustrates a variant of the second embodiment described withreference'to FIG. 4. The principle variation is the provision of morethan one tubular electroexpansive element. The first element 61 issubstantially the same as the single element 44 shown in FIG. 4 with anelectrical connection between the signal source 45 and the insidesurface of the element 61 and between the outside surface of element 61and the body 40' by a spring 63. Connections are provided for a secondtubular electroexpansive element 64 in a corresponding but reversemanner with the inside surface thereof connected to the body 40 by aspring 65, and the outside surface directly connected to the signalsource 45. In that manner, multiple electroexpansive elements may beused to provide increased fluid displacement. Another variation is theprovision ofa piston 66 and pump valving means 67 in a manner similar tothat described with reference to FIG. 3 for the first embodiment of thepresent invention such that volume amplification is achieved.

A third embodiment of the present invention is illustrated in FIG. 7. Itconsists of a body 70 having a cylindrical chamber in which segmentalsections of electroexpansive elements are radially disposed, such as asection 71 shown in an isometric view in FIG. 8. As viewed in that FIG.8, the top surface is coated with a conductor 72, such as silver, aroundto the far, narrow end. The bottom side is similarly coated with aconductor 73 around to the near, wide end. By applying a potentialacross the two ends, an electric field is established between theconductors 72 and 73. Accordingly, when segmental sections have been soplaced in the chamber of the body 70 that adjacent ones have theirconductors 72 opposite each other and similarly have their conductors 73opposite each other, a signal may be applied to all of the sections inparallel by a source 74. The elements expand circumferentially withlittle or no radial contraction for a net volume increase. In thatmanner, fluid may be driven out of the chamber of the body 70. A pumpvalving means 75 (the same as that described with reference to FIG. 1)is provided in order that the electroexpansive driver may pump fluidfrom an inlet port 76 to an outlet port 77.

A tube 78 is provided as a central column in the chamber of the body 70to assure that the segmental sections'remain in place substantially asshown in FIG. 7 with the wide end of each in contact with thecylindrical wall of the body 70. A split ring 79 of conductive springmaterial is placed around the column 78, as may be more clearly seen inFIG. 9. As the split ring 79 seeks to expand in diameter, the segmentalsections are maintained in electrical contact with the cylindrical wallof the body 70. At the same time, the split ring 79 is in contact withthe narrow end of each segment so that it may be employed as oneelectrode connected to the signal source 74 as shown in FIG. 7 while thecylindrical wall of the body 70 is employed as the other (ground)electrode. The tube 78 is provided with a plurality of holes, such as ahole 80, in order that pressures quickly equalize throughout the chamberof the body 70.

If the fluid being pumped is an electrical conductor, a nonconductivehydraulic fluid may be provided in the chamber of the body 70 andisolated from the fluid being pumped by a piston in the manner describedhereinbefore with reference to FIG. 2 or, if volume amplification isdesired, in a manner described hereinbefore with reference to FIG. 3.Alternatively, the pump valving means 75 may be omitted and a valve orother device attached to the body 70 for actuation through a piston in amanner similar to that described hereinbefore with reference to FIG. 4.

Although the pump valving means 75 is shown in FIG. 7 connected to aradial passage from the chamber of the body 70, it should be appreciatedthat such a means or other device may be connected to an axial passageas shown in FIG. 10 by a pump valving means 81 connected to a body 82which is otherwise the same as that illustrated in FIG. 7. In thatmanner, the passage from chamber of the body 82 to the valving means 8]is through the center of an end wall to provide direct fluid transferfrom a central tube of the form illustrated in FIG. 9. Here again, thepump valving means 81 may be isolated from the hydraulic fluid in thechamber of the body 82 by a piston, and may also be substituted with apiston actuated device ifdesired.

Although the present invention has been shown and described withreference to particular embodiments, it should be apparent to oneskilled in the art that many changes and modifications may be madewithout departing from the true spirit and scope of the invention.

What is claimed is:

1. An electroexpansively powered fluid driver comprising:

a body having a chamber of a given volume and a passage in a wallthereof communicating with said chamber; volumetric electroexpansivematerial disposed in said chamber, said material being a solid andhaving a total volume less than said given volume ofsaid chamber;

nonconductive fluid filling said chamber and in direct contact with saidelectroexpansive material on all sides free to move in response to anelectric field applied to said electroexpansive material such that allof said fluid will be at the same pressure at any given time; and

means for applying an electric signal as a potential across saidmaterial to create said electric field to cause said material to undergoa total volume change to perform work by forcing fluid from said chamberthrough said passage.

2. Apparatus as defined in claim 1 including pump valving meanscomprising:

a pump chamber having a port connected to said passage;

fluid inlet means having a one-way valve communicating with said pumpchamber; and

fluid outlet means having a one-way valve communicating with said pumpchamber.

3. Apparatus as defined in claim 1 wherein said chamber is a cylinderand said material is in the form of a plurality of segmental sections,said sections being disposed about a central spring tube through whichelectrical contact is made with each section while each section is beingurged against the cylindrical wall of said chamber, said wall being madeof electrical conductive material, and said means is connected betweensaid spring tube and said cylindrical wall.

4. Apparatus as defined in claim 3 including pump valving meanscomprising:

a pump chamber having a port connected to said passage;

fluid inlet means having a one-way valve communicating with said pumpchamber; and

fluid outlet means having a one-way valve communicating with said pumpchamber.

5. An electroexpansively powered driver comprising:

a hydraulic cylinder;

a body having an hydraulic fluid chamber of a given volume and a passagein a wall thereof communicating with said hydraulic cylinder;

volumetric electroexpansive material so disposed in said chamber as toprovide a hydraulic drive chamber between said material and walls ofsaid chamber;

a piston disposed in said cylinder;

fluid filling said hydraulic drive chamber and passage to said piston insaid cylinder, said fluid surrounding said electroexpansive material onall sides free to move in response to an electrical field applied tosaid electroexpansive material such that all of said fluid will be atthe same pressure at any given time; and

means for applying an electric field to said material to cause saidmaterial to undergo a total volume increase to hydraulically advancesaid piston in said cylinder.

6. Apparatus as defined in claim 5 including pump valving meanscomprising:

a pump chamber having a port connected to said cylinder at the endthereof remote from said hydraulic drive chamber;

fluid inlet means having a one-way valve communicating with said pumpchamber; and

fluid outlet means having a one-way valve communicating with said pumpchamber;

7. Apparatus as defined in claim 6 including a return spring in saidcylinder between said piston and said pump valving means.

8. Apparatus as defined in claim 5 wherein said piston has a portion atone end thereof with an area that differs from the area at the other endthereof, and said cylinder is of a diameter substantially equal to thatof said portion over a sufficient length thereof to receive said portionof said piston and allow maximum travel of said piston.

9. Apparatus as defined in claim 8 including means for venting saidcylinder at the base of the enlarged portion thereof.

10. An electroexpansively powered fluid driver comprising:

a hydraulic cylinder;

a body having an annular hydraulic fluid chamber of a given volume and apassage in a wall thereof communicating with said hydraulic cylinder;

at least one tube of volumetric electroexpansive material so disposed insaid chamber as to provide a hydraulic drive chamber between said tubeand walls of said body;

an actuating piston disposed in said cylinder;

fluid filling said hydraulic drive chamber and passage to said piston insaid cylinder, said fluid surrounding said electroexpansive material onall sides free to move in response to an electrical field applied tosaid electroexpausive material such that all of said fluid will be atthe same pressure at any given time; and

means for applying said electric field to said material to tending fromsaid cylinder for actuation of a device.

12. Apparatus as defined in claim 11 wherein said device is a valve andthe end of said arm remote from said piston comprises a valving plunger.

13. Apparatus as defined in claim 11 wherein said device is a pump andthe end of said arm remote from said piston comprises a pumping piston.

14. Apparatus as defined in claim 13 wherein said pumping piston has adiameter that differs from the diameter of said actuating piston.

15. Apparatus as defined in claim 10 wherein a second tube of volumetricelectroexpansive material is disposed in said chamber and said meansfunctions for said second tube in the same manner as for said one tubeof volumetric electroexpansive material.

1. An electroexpansively powered fluid driver comprising: a body havinga chamber of a given volume and a passage in a wall thereofcommunicating with said chamber; volumetric electroexpansive materialdisposed in said chamber, said material being a solid and having a totalvolume less than said given volume of said chamber; nonconductive fluidfilling said chamber and in direct contact with said electroexpansivematerial on all sides free to move in response to an electric fieldapplied to said electroexpansive material such that all of said fluidwill be at the same pressure at any given time; and means for applyingan electric signal as a potential across said material to create saidelectric field to cause said material to undergo a total volume changeto perform work by forcing fluid from said chamber through said passage.2. Apparatus as defined in claim 1 including pump valving meanscomprising: a pump chamber having a port connected to said passage;fluid inlet means having a one-way valve communicating with said pumpchamber; and fluid outlet means having a one-way valve communicatingwith said pump chamber.
 3. Apparatus as defined in claim 1 wherein saidchamber is a cylinder and said material is in the form of a plurality ofsegmental sections, said sections being disposed about a central springtube through which electrical contact is made with each section whileeach section is being urged against the cylindrical wall of saidchamber, said wall being made of electrical conductive material, andsaid means is connected between said spring tube and said cylindricalwall.
 4. Apparatus as defined in claim 3 including pump valving meanscomprising: a pump chamber having a port connected to said passage;fluid inlet means having a one-way valve communicating with said pumpchamber; and fluid outlet means having a one-way valve communicatingwith said pump chamber.
 5. An electroexpansively powered drivercomprising: a hydraulic cylinder; a body having a hydraulic fluidchamber of a given volume and a passage in a wall thereof communicatingwith said hydraulic cylinder; volumetric electroexpansive material sodisposed in said chamber as to provide a hydraulic drive chamber betweensaid material and walls of said chamber; a piston disposed in saidcylinder; fluid filling said hydraulic drive chamber and passage to saidpiston in said cylinder, said fluid surrounding said electroexpansivematerial on all sides free to move in response to an electrical fieldapplied to said electroexpansive material such that all of said fluidwill be aT the same pressure at any given time; and means for applyingan electric field to said material to cause said material to undergo atotal volume increase to hydraulically advance said piston in saidcylinder.
 6. Apparatus as defined in claim 5 including pump valvingmeans comprising: a pump chamber having a port connected to saidcylinder at the end thereof remote from said hydraulic drive chamber;fluid inlet means having a one-way valve communicating with said pumpchamber; and fluid outlet means having a one-way valve communicatingwith said pump chamber.
 7. Apparatus as defined in claim 6 including areturn spring in said cylinder between said piston and said pump valvingmeans.
 8. Apparatus as defined in claim 5 wherein said piston has aportion at one end thereof with an area that differs from the area atthe other end thereof, and said cylinder is of a diameter substantiallyequal to that of said portion over a sufficient length thereof toreceive said portion of said piston and allow maximum travel of saidpiston.
 9. Apparatus as defined in claim 8 including means for ventingsaid cylinder at the base of the enlarged portion thereof.
 10. Anelectroexpansively powered fluid driver comprising: a hydrauliccylinder; a body having an annular hydraulic fluid chamber of a givenvolume and a passage in a wall thereof communicating with said hydrauliccylinder; at least one tube of volumetric electroexpansive material sodisposed in said chamber as to provide a hydraulic drive chamber betweensaid tube and walls of said body; an actuating piston disposed in saidcylinder; fluid filling said hydraulic drive chamber and passage to saidpiston in said cylinder, said fluid surrounding said electroexpansivematerial on all sides free to move in response to an electrical fieldapplied to said electroexpansive material such that all of said fluidwill be at the same pressure at any given time; and means for applyingsaid electric field to said material to cause said material to undergo atotal volume increase to hydraulically advance said piston in saidcylinder.
 11. Apparatus as defined in claim 10 including an armextending from said cylinder for actuation of a device.
 12. Apparatus asdefined in claim 11 wherein said device is a valve and the end of saidarm remote from said piston comprises a valving plunger.
 13. Apparatusas defined in claim 11 wherein said device is a pump and the end of saidarm remote from said piston comprises a pumping piston.
 14. Apparatus asdefined in claim 13 wherein said pumping piston has a diameter thatdiffers from the diameter of said actuating piston.
 15. Apparatus asdefined in claim 10 wherein a second tube of volumetric electroexpansivematerial is disposed in said chamber and said means functions for saidsecond tube in the same manner as for said one tube of volumetricelectroexpansive material.